The invention relates to an exhaust-gas turbocharger including a compressor and a turbine disposed in a housing with multiple exhaust gas supply passage of which some can be closed by adjustable shut-off flaps.
The publication US 18 16 787 describes a multi-cylinder internal combustion engine, which is equipped with an exhaust-gas turbocharger, which comprises a compressor in the inlet duct of the internal combustion engine and an exhaust-gas turbine in the exhaust duct. The exhaust gas turbine is driven by the pressurized exhaust gases from the internal combustion engine, the rotation of the turbine being transmitted, by way of a common shaft, to the compressor, which draws in the combustion air and compresses it to an increased charge-air pressure, under which the combustion air is delivered to the cylinder inlets of the internal combustion engine. In order to be able to adjust the turbocharger output, the exhaust gas is delivered to the turbine rotor by way of three flow ducts, in each of which a valve is arranged, whose position can be adjusted by way of a common control rod as a function of the charge-air pressure, so as to compensate for pressure fluctuations. No provision is made here for any independent adjustment of the opening cross section of each flow duct, the valves in the flow ducts instead being opened or closed in a set order through the actuation by means of the control rod. In the exhaust-gas turbocharger according to US 18 16 787 no further adjustment facilities are provided other than the atmospheric pressure compensation.
Another problem is that the shut-off valves in the flow ducts are designed as pivoted flaps, the pivot axes of which extend approximately centrally through the respective flow duct, so that even in its open position the shut-off valve forms an obstacle to the flow of the exhaust gas.
Another exhaust-gas turbocharger is disclosed by the generic publication DE-AS 1 253 510. The exhaust-gas turbine of this exhaust-gas turbocharger comprises two parallel exhaust manifolds, which each open into a spiral section, which radially surrounds part of the turbine rotor. A pivotal shut-off flap, which can be pivoted between a shut-off position closing the flow inlet of the exhaust manifold and an open position exposing it is arranged in the area of the flow inlet of one of the two exhaust manifolds. In the open position, the shut-off flap is accommodated in a correspondingly shaped recess in the inside wall of the turbocharger housing, thereby avoiding any adverse effect on the flow of exhaust gas entering. No shut-off flap is provided in the area of the second exhaust manifold; the second exhaust manifold remains permanently opened.
For adjustment of the turbocharger output, the shutoff flap can be adjusted between its open position and its shut-off position, so that given an identical cross section in both exhaust manifolds the total unrestricted inlet cross section available to the exhaust gas inlet flow can be approximately doubled.
It is the main object of the invention to provide an exhaust-gas turbocharger that is variably adjustable.
In an exhaust-gas turbocharger having a compressor and an exhaust-gas turbine, which drives the compressor and comprises a multi-part exhaust gas supply duct manifold and a turbine rotor, to which pressurized exhaust gas can be delivered by way of the exhaust gas supply duct, the exhaust gas supply duct manifold includes at least three flow passages, which, except for one, are provided with shut-off flaps, which are adjustable independently of one another.
This arrangement allows a maximum number of adjustments for the admission of exhaust gas to the turbine rotor to be achieved using a minimum number of shut-off flaps. The independent adjustment of the shut-off flaps enables the existing flow ducts to be interconnected in any combination, in order to provide a greater or lesser overall cross section for the delivery of exhaust gas, at least the one flow duct having no flap being permanently open, so that a minimum of exhaust gas is delivered to the exhaust gas turbine in any operating condition of the internal combustion engine.
A further advantage lies in the simplicity of the design. In contrast to exhaust-gas turbines having a variable turbine geometry achieved, for example, by means of a guide baffle with adjustable guide vanes, so that a multiplicity of moveable components have to be adjusted, which increase the susceptibility to malfunction, in the simplest design of the exhaust-gas turbocharger according to the invention, having a total of three flow ducts, only two shutoff flaps are needed, which are arranged in two of the three flow ducts for adjustment of the unrestricted inlet cross section. This reduces the number of moving parts considerably. At the same time, however, the various possible combinations of opened and closed shut-off flaps, available even in the simplest version with three flow ducts, mean that up to four different-sized overall inlet cross sections can be set for the delivery of exhaust gas, which is usually sufficient for all operating conditions both during engine power operation and during engine braking of the vehicle.
Through an adept choice of inlet cross sections for the flow ductsxe2x80x94such as two flow ducts of equal cross section, one flow duct with a cross section twice as large, for examplexe2x80x94four overall inlet cross sections, divided up in the size ratio 1:2:3:4, can be exposed for the various operating conditions of the internal combustion engine.
In an advantageous embodiment, at least two shut-off flaps are arranged in the two outer flow ducts, and supported so that they are capable of pivoting onto the inside wall of the turbine housing. In this design at least one flow duct, situated in the middle between the two outer ducts, is designed without a flap, the middle flow duct and the two outer flow ducts in each case sharing a common wall in the event of there being a total of just three flow ducts.
The shut-off flaps are advantageously designed to conform to the contour of the inside wall of the turbine housing and in the open position fit precisely against the inside wall, thereby presenting the least possible flow resistance to exhaust gas flowing in. The outside of the shut-off flap remote from the inside wall of the turbine housing and facing the flow duct may here have a flow-enhancing contour in order to further minimize the flow resistance and to obtain any desired flow effects, such as an acceleration of the flow through tapering of the unrestricted inlet cross section.
It may also be appropriate, however, to incorporate a recess, designed to conform to the shut-off flap, into the inside wall, in which recess the shut-off flap can be received in the open position. In this design the shut-off flap in the open position can be fully accommodated in the recess, thereby providing for a smooth inside wall surface.
In order to improve the flow ratios over the turbine rotor a fixed guide baffle may be provided in a duct upstream of the turbine rotor, the duct being connected to, or being part of, the exhaust manifold. In an alternative version, the guide baffle may also be variably adjustable, being axially insertable into the guide channel, for example, or equipped with adjustable guide vanes. A variable turbine geometry is thereby achieved, which permits a multiplicity of possible adjustments of the unrestricted inlet cross section.
The exhaust manifoldxe2x80x94with or without guide bafflexe2x80x94is advantageously divided into a plurality of angular sections, which are hermetically separated from one another, precisely one angular section in the guide channel being assigned to each flow duct. The ratio of the angular sections advantageously corresponds to the ratio of the flow duct cross sections, so that a double angular section is also assigned to the flow duct having twice the cross section.
The invention will become more readily apparent from the following description thereof on the basis of the accompanying drawings: